The present invention relates to a method of preparing a polymer with reduced solubility in an organic solvent from a polymer that is soluble in the solvent by virtue of the presence of solubilizing groups which, when removed or converted to nonsolubilizing groups, form the polymer that has reduced solubility in the solvent.
Electroactive polymers such as conjugated polymers containing structural units of a fluorene monomer are useful as thin films in electronic devices such as organic light emitting diode displays (OLEDs) or transistors. Typically, a solution of an electroactive polymer such as poly(9,9-dioctyl fluorene-alt-bithiophene) dissolved in xylenes is applied to a substrate by techniques such as spin coating or ink jet printing, whereupon solvent is removed to form a thin film of the soluble polymer with desirable electroactive properties. The presence of the octyl groups on the fluorene structural units of the polymer imparts solubility and improves the handling characteristics of the polymer, but may disadvantageously degrade the transport characteristics and prevent the formation of ordered microstructure in the final film.
Although polymer films containing ordered microstructure are clearly desired, polymers that intrinsically develop such structure tend to be insoluble in precursor ink solutions. Therefore, applying these preferred polymers to substrates by solution processing is impractical if not impossible. While it is possible to apply an insoluble polymer onto a substrate by means such as evaporation, sputtering, or plasma enhanced chemical vapor deposition, these techniques are slow and expensive.
Consequently, it would be desirable to prepare an insoluble electroactive organic film on a substrate from a material that can be easily and reproducibly applied to the substrate.